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Some say turn engine off at long signals while others say it wastes more gas to turn the engine off and on. Which has PROVEN to be correct?

Restarting the engine uses as much gas as 10 seconds of idling.

Stargift, your concerns might have been justified back in the days of carburetion, but virtually zero cars on the road are carbureted anymore. A fuel injected engine revs a bit and runs slightly richer for a couple of seconds after restart, but the extra fuel is the equivalent of 10-15 seconds of idling.

And you can lessen even the 10-15 second figure by waiting to restart until you're ready to roll. If you use that extra squirt of fuel towards moving the car forward, then even that fuel isn't going to waste.

Remember, that's how hybrids work. To my knowledge, there's nothing different about a hybrid in terms of its fuel injection programming that makes its ICE behave any differently than any other engine on a warm start. The ability to kill and restart the engine as appropriate is one of the 3 main reasons hybrids get better fuel economy.

My rule of thumb: I often don't bother killing the engine at short, simple lights. Longer, more complex lights with multiple left turn signals almost always call for a shutdown unless it's a stale red that I know will turn soon.

Stargift, as you "learn" the lights, you will be better able to make a decision to turn off the engine or not. Also, if you do turn off the engine, try to see the cross traffic light, to see when it is changing to yellow. That gives you some heads up on a re-start. Might take a while to learn the lay of the land, so go easy and keep your comfort level.

Anticipation is key here -- the earlier you realize you'll have to stop, the further back you can FAS and the more fuel you can save in the process. It is rare indeed that I get a FAS in that is anywhere close to 10s short.

Stargift,

If you are looking for proofs in hypermiling, they will be difficult to find. The problem is, there are too many variables and even a difference of a half gallon in filling the tan